Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens, and in particular, to a zoom lens that can be used as an image pickup optical system of an image pickup apparatus, such as a digital still camera, a video camera, a monitoring camera, a broadcast camera, or a film camera.
Description of the Related Art
It is required that a zoom lens used as image pickup optical system of an image pickup apparatus have a high optical performance. For example, for a zoom lens of a monitoring camera, it is required that the zoom lens have a super-wide view angle so that a wide area can be monitored with a single monitoring camera. Moreover, it is required that the zoom lens have a small F-number so that a clear image can be captured even at night. Furthermore, it is required that the entire zoom lens be small so that the monitoring camera can be easily set inconspicuously in monitoring locations.
Two-unit zoom lenses are known that include, from the object side to the image side, a first lens unit having a negative refractive power and a second lens unit having a positive refractive power. Two-unit zoom lenses perform zooming by moving the first and second lens units. Japanese Patent Application Laid-Open No. 8-320435 describes a small zoom lens having an angle of view of about 80 degrees at the wide angle end, an F-number of 2 at the wide angle end, and a zoom ratio in the range of about 3 to 6. Japanese Patent Application Laid-Open No. 2009-204699 describes a small zoom lens having an angle of view of about 140 degrees at the wide angle end, an F-number of 1.2 at the wide angle end, and a zoom ratio of about 3.5.